1. Field of the Invention
The present invention relates to a photosensitive resin composition, and to a flexible printed wiring circuit board having an insulative cover layer formed of the photosensitive resin composition.
2. Description of the Related Art
An electrically conductive pattern of a flexible printed wiring circuit board on which an electronic component such as a semiconductor device is mounted by soldering is generally covered with an insulative cover layer formed, for example, by applying a heat resistant material such as a solder resist on the electrically conductive pattern by a screen printing method or an exposure/development method.
Typically usable as the solder resist is a photosensitive resin composition, for example, containing a carboxyl-containing linear polymer, a photopolymerizable monomer, a cyclic phosphazene compound (flame retarder), a pigment and the like (see, for example, JP-A-2006-235371).
When the flexible printed wiring circuit board having the insulative cover layer formed of the aforementioned solder resist (photosensitive resin composition) is allowed to stand under high temperature and high humidity conditions, components of the solder resist are liable to be deposited on the wiring circuit board to contaminate a product which incorporates the circuit board. Particularly, the cyclic phosphazene compound flame retarder is most liable to be deposited on the wiring circuit board. Therefore, it is desired to prevent the deposition of the cyclic phosphazene compound as well as to improve the flame resistance, the flexibility and the resolution of the solder resist.
In view of the foregoing, it is an object of the present invention to provide a photosensitive resin composition which is excellent in flame resistance, resolution, warp resistance and flexibility when used for a flexible printed wiring circuit board, and is substantially free from deposition of components thereof to prevent contamination of a product incorporating the flexible printed wiring circuit board, and to provide a flexible printed wiring circuit board having an insulative cover layer formed of the photosensitive resin composition.